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Re: ext3 with maildir++ = huge disk latency and high load



Let me to share some testing RAID 5 results with bonnie++:

ext3 (defaults,noatime):

Version 1.96 ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP debian 2G 242 96 22458 10 8826 2 1854 98 120985 11 317.1 3 Latency 211ms 896ms 720ms 22258us 18733us 622ms Version 1.96 ------Sequential Create------ --------Random Create-------- debian -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 16 12857 33 +++++ +++ 15377 34 13585 33 +++++ +++ 15404 35 Latency 12284us 992us 1029us 432us 140us 76us

ext3 (-T small,defaults,noatime):

Version 1.96 ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP debian 2G 229 98 4989 5 3862 1 1762 97 91111 9 266.6 6 Latency 79046us 22858ms 2577ms 19253us 12120us 767ms Version 1.96 ------Sequential Create------ --------Random Create-------- debian -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 16 6422 16 +++++ +++ 10319 25 8934 21 +++++ +++ 10347 26 Latency 9968us 977us 964us 482us 144us 178us

ext3 (-T news,defaults,noatime):
Version 1.96 ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP debian 2G 237 95 22807 11 8807 2 1897 99 121893 11 324.6 5 Latency 223ms 808ms 523ms 13765us 11049us 831ms Version 1.96 ------Sequential Create------ --------Random Create-------- debian -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 16 12826 33 +++++ +++ 15900 35 14548 36 +++++ +++ 15460 35 Latency 417us 984us 1024us 430us 140us 175us

ext4 (defaults,noatime):

Version 1.96 ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP debian 2G 256 98 21495 6 9896 2 1771 99 125775 11 349.7 5 Latency 37738us 992ms 3490ms 10811us 12045us 495ms Version 1.96 ------Sequential Create------ --------Random Create-------- debian -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 16 14766 43 +++++ +++ 18026 46 16094 46 +++++ +++ 17428 45 Latency 424us 982us 1023us 367us 139us 174us

xfs(defaults,noatime,logbufs=8,logbsize=131072):

Version 1.96 ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP debian 2G 476 96 35129 9 12524 3 1417 99 124716 12 445.9 9 Latency 19798us 420ms 721ms 14122us 9394us 131ms Version 1.96 ------Sequential Create------ --------Random Create-------- debian -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 16 1552 8 +++++ +++ 1705 11 1675 9 +++++ +++ 1346 8 Latency 104ms 291us 48604us 109ms 45us 227ms

It seems that latency is big in whole results, best is for XFS. It is tempting me to think that there are some RAID 5 issues here. It's really strange that block writing for SCSI server disks in RAID5 is no more than 30MB/sec(XFS). I guess I should consider XFS file system or different RAID configuration. May be someone can comment this strange benchmark result? Will very appreciate that.

With regards, Andrey.

23.09.2011 11:31, Janne Pikkarainen пишет:
Hello,

On 09/23/2011 08:51 AM, Andrey wrote:
Hello,

I have a production mail server with maildir++ structure and about
250GB (~10 millions) of files on the ext3 partition on RAID5. It's
mounted with noatime option. These mail server is responsible to local
delivery and storing mail messages.

System has Debian Squeeze installed and Exim as MDA + Dovecot as
IMAP+POP3 server.

Bonnie results are terrible. Sequential output for Block and Rewrite
are 10722ms and 9232ms. So if there is a 1000 messages in the mail
queue load is extremely high, delivery time is very big and server can
hang. I did not see such problems with UFS on FreeBSD server.

As I understand ext3 file system is really bad for such configurations
with Maildir++ (many smaill files)? Is there a way to decrease disk
latency on ext3 or speed up it?

With regards, Andrey

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